Depending on how they are cooked, hamburgers are a delicious, succulent food, and as a result, many restaurants all across the country specialize in serving this singular menu item. It is well known that the ingredients which contribute to the unique taste of hamburger are the fats and meat juices. Beef tallow, however, has a relatively low solidification point within the range of 88.degree.-100.degree. F. and, therefore, hamburgers are preferably formed into relatively thick patties and cooked at relatively low temperatures to prevent the tasty fats and meat juices from being melted or boiled away. Nonetheless, for reasons explained more fully hereinafter, fast food restaurants have found it commercially expedient to use relatively thin patties and cook them at relatively high temperatures in order to reduce the preparation time.
At the present time there are a wide variety of fast good restaurants which sell hamburgers and similar food items. Necessary to the success of such fast food operations is the ability to rapidly cook, garnish and serve hamburgers. Hamberger meat, however, it has become an accepted practice in the fast food industry to roll or press hamburgers into relatively thin patties, usually less than one-fourth inch, in order to decrease the amount of time necessary to cook them thoroughly. In particular, it has been found that by reducing the thickness of the hamburger patties, the distance the heat must travel through each patty is reduced, thereby reducing the amount of time necessary to cook the meat.
Though tastes differ, in general, the interior of a hamburger patty must be heated to a temperature of 160.degree. F. before it is considered sufficiently done. To rapidly achieve this interior temperature, the exterior surfaces of the hamburger patty are subjected to relatively high temperatures, generally between 325.degree. and 600.degree. F. For example, the interior of a hamburger patty having a thickness of one-fourth inch can be heated to the desired temperature of 160.degree. F. by exposing each side to temperatures of about 350.degree. for 60 to 75 seconds. Establishments which cook hamburgers in this manner sometimes utilize an open griddle which is operated by at least one attendant. As such, a relatively large amount of heat energy and a relatively large amount of manpower is required to prepare hamburgers in manner.
During cooking on an open grill, however, there is a tendency for the hamburger patty to crawl together, shrink in diameter, and become thick in the center. This not only creates an undesirable appearance, it also creates cooking problems because the increased thickness requires higher temperatures, longer cooking time, or both. Increasing the cooking conditions tend to reduce the amount of fat and juices in the patty so that there not only a weight loss, but the product also tends to have a dry taste.
A popular alternative to the grill method of preparing hamburgers is the use of filed on broiler having heating elements inside a cabinet or hotbox. A chain conveyor carries the hamburger patties through the hotbox, and by adjusting the speed of the conveyor, the thickness of the hamburger patties, and the temperature of the heating elements, the hamburger patties can be rapidly cooked to the desired temperatures with minimal supervision. The temperatures of the heaters used in hotboxes of the type described varies between 350.degree. and 700.degree. F., but since the heaters can be disposed above and below the chain conveyor, the hamburger can be heated on both sides simultaneously, or consecutively. As a result, hamburgers are cooked by the broiler method in approximately half of the time normally required by the grill method, and with a minimal amount of manpower.
Though the broiler method of cooking hamburger is successfully used in fast food restaurant operations, it is also subject to numerous drawbacks. There are a number of variable conditions in the broiler which as a practicable matter must remain fixed; namely, speed of the conveyor and the temperatures of the heaters; and this has disadvantages. For example, it is commercially impracticable to cook hamburgers of both thin one-fourth inch and thick three-fourth inch sizes by the broiler method because that necessitates changing cooking conditions which is impracticable.
Most importantly, both the grill method and the broiler method of cooking hamburgers rely on the relatively slow process of heat conduction through the hamburger patty itself. Thus, while one must wait for the interior of the hamburger patty to reach the desired 160.degree. F. even with a thin one-fourth inch thick patty, the exterior portions are being directly exposed to relatively high temperatures for up to 75 seconds. During this period of time, the fats and meat juices located near the more exterior portions of the hamburger patty are melted or boiled away, causing a noticeable loss of taste. In addition, a substantial amount of shrinkage results, a factor of increasing importance in an era of burgeoning meat prices.
For all these reasons, the hamburger prepared in fast food operations in often characterized by relatively thin, shriveled patties having a bland taste. In contrast to the hamburgers prepared in fast food restaurants, the hamburgers prepared in the home, where high speed preparation is not of the essence, are often thicker, juicier, and tastier. The primary reason for this difference is that hamburgers prepared at home can be cooked slowly at temperatures not in excess of 250.degree. F. The relatively long period of time required to produce such a product is wholly impractical for fast food operations, and therefore, a compromise in taste and thickness must be made.